There is a strong demand to reduce the size of electronic systems. Size reduction is especially desirable in mobile electronics in which space is a premium, but is also desirable in servers that are placed in big data centers since it is important to squeeze in as many servers as possible into fixed-size real estate.
Some of the largest components in electronic systems are voltage regulators (also referred to as power regulators). Voltage regulators often include a large number of bulky off-chip components to deliver voltages to integrated chips, including processors, memory devices (e.g., a dynamic random access memory (DRAM)), radio-frequency (RF) chips, WiFi combo chips, and power amplifiers. Therefore, it is desirable to reduce the size of voltage regulators in electronic systems.
Voltage regulators include semiconductor chips, such as DC-DC regulator chips, that each deliver power from a power source (e.g., a battery) to an output load. The output load can include a variety of integrated chips (e.g., an application processor, a DRAM, a NAND flash memory, etc.) in an electronic device.
To efficiently deliver power, a voltage regulator can use a “buck” topology. Such a regulator can be referred to as a buck regulator (also referred to as a buck converter). A buck regulator transfers charge from a power source to an output load using an inductor. A buck regulator can use power switches to rapidly connect/disconnect an inductor to/from multiple voltages (each at a different point in time), thereby providing an output voltage that is a weighted average of the multiple voltages. A buck regulator can adjust the output voltage by controlling the amount of time the inductor is connected to each of the multiple voltages.
Unfortunately, a buck regulator is not suitable for highly integrated electronic systems. The conversion efficiency of a buck regulator depends on the size of its inductor, in particular when the power conversion ratio is high and when the amount of current consumed by its output load is high. Because an inductor can occupy a large area and is bulky to integrate on-die or on-package, existing buck regulators often use a large number of off-chip inductor components. This strategy often requires a large area on a printed circuit board on which an existing buck regulator and its corresponding off-chip inductor components are located, which in turn increases the size of an electronic device in which the printed circuit board is located. The challenge is exacerbated as mobile system-on-chips (SoCs) become more complex and need increasingly larger number of voltage domains to be delivered by their voltage regulators.
Furthermore, a buck regulator is not well suited for high-speed charging of a battery. High-speed charging generally requires the use of a high input voltage. The use of a high input voltage, in turn, requires the buck regulator to provide a high voltage conversion ratio (VIN/VOUT) to convert a high input voltage (VIN) to an output voltage (VOUT) that is suitable for batteries. Unfortunately, at a high voltage conversion ratio, the efficiency of the buck regulator is relatively low when compared to other types of voltage regulators, at least in part because the buck regulator wastes a large amount of power through heat dissipation. The heat dissipated by a buck regulator may raise the operating temperature of devices within an electronic system, which could cause malfunctioning. Therefore, buck regulators are not well suited for high-speed charging of batteries.
Instead of a buck regulator, a high-speed charging system may use a switched-capacitor regulator to charge a battery. A switched capacitor regulator is known to be efficient even at a high voltage conversion ratio as long as the voltage conversion ratio is an integer number. Unfortunately, existing charging systems do not include a mechanism for keeping the conversion ratio of a switched capacitor regulator at an integer number, and hence, the high efficiency of a switched capacitor regulator cannot be maintained across operating conditions. Therefore, there is a strong need to provide a charging system that is capable of maintaining a high efficiency at high input to output conversion ratios.